Epithelial cells lining the mammalian trachea form a crucial site in the host defense against airborne microbial pathogens, releasing numerous antimicrobial factors. Deficiencies in these defenses may result in recurrent airway infections. One of these defense mechanisms is the inducible production of beta-defensins, a class of homologous antibiotic peptides highly abundant in mammalian epithelial cells. The genes encoding beta-defensins are expressed at high levels in the respiratory epithelium, and are induced by bacterial products and inflammatory mediators. Preliminary and published data support the hypothesis that some pathogenic strains of bacteria can evade the innate immune system in the airway by inhibiting beta-defensin gene expression, which can in turn diminish the antimicrobial defense of the airway. The mechanisms by which the specific bacterial virulence factors allow evasion of the first lines of host defense to colonize the airway are not yet defined. Elucidation of these mechanisms will aid in the development of therapeutic strategies for airway infections. The long-range goal of our research is to better understand the dynamic host defense systems in the airway. In this proposal we focus on the interactions of the airway pathogen, Bordetella bronchiseptica with its target cells in the respiratory epithelium. B. bronchiseptica is associated with respiratory infections in animals, and is closely related to B. pertussis, the causative agent of whooping cough in humans. We hypothesize that airway epithelial cells respond to bacteria by recognition of molecular patterns by specific receptors, resulting in the activation of NF-kappaB and induction of beta-defensin gene expression in order to prevent colonization. Pathogenic strains of B. bronchiseptica can prevent the increased production of antimicrobial peptides by interfering with the upregulation of the antimicrobial peptide genes through a type III secretion factor which interferes with the innate immune response. To test these hypotheses, the following aims are proposed: 1. Define the interaction of B. bronchiseptica with airway epithelial cells and the resultant induction of an innate immune response. 2. Define the mechanism of inhibition of innate immune induction by virulent B. bronchiseptica. The objective of these studies is to define how the airway epithelium responds to this model pathogen by the initiation of a host defense response. The second aim will determine how the bacterium circumvents this response utilizing proteomics to identify the bacterial factor responsible for this action, as well as a comprehensive characterization of the interaction of this factor and the defense response. The information will serve as a foundation for the development of novel therapies designed to work in the respiratory tract. This would include strategies to modulate the endogenous antimicrobial peptide expression to prevent serious bacterial infections.